Format

The rel=vcs-* microformat can only appear in the html <link> element in
the <head> of the page, or in an <a> element in its body.

The rel attribute specifies what VCS is used. It can contain the name
of any version control system, prefixed with "vcs-".
Common values include "vcs-git", "vcs-svn", and "vcs-bzr".

The "href" holds a URI, or other location identifier, in a format
supported by the version control system. If a version control system
supports both URIs and some other location identifier form, the URI form
is strongly preferred here. Making up URI forms just for use here is,
however, discouraged.

The "title" is optional, but recommended if there are multiple, different
repositories linked to on one page. It is a human-readable description of
the repository. If the title is omitted from an <a> tag, the body of the tag
should be a human-readable description.

Multiple repositories

Since many version control systems use one URI form (such as git:// or
http://) for anonymous access, and another form (such as ssh:// or
svn+ssh://) for authenticated access, multiple <link> or <a> tags can
be used on the same page, to list each available URI. When this is done,
the same text should be used for the title parameter of each repository.
For example:

Tools that process the microformats can assume that repositories listed on
the same page, with the same title, each contain the same data. Such tools
can choose which repository to use based on the type of URI it uses (for
example by preferring git://, then http://, and finally ssh://).

If there are multiple repositories listed, without titles, tools should
assume they are different repositories.

Producers

A website for a software package can use the rel=vcs-* microformat
on its front page, and on any relevant download pages, to indicate the
location of its VCS repository.

A VCS repository browser such as ViewVC or gitweb can use the rel=vcs-*
microformat on pages it generates, to specify the location of the
repository being browsed.

Related efforts and motivations

The Debian project added VCS-* fields to their source packages,
indicating the repository used to develop each package, and many useful
tools sprang up to take advantage of this information, such as
debcheckout, which can automatically check out the source to a package
from its VCS.